Suggest that fish users init in interactive mode
Suggest that fish users init in interactive mode

...rather than login mode.

I couldn't get rid of the warning that `pyenv init -` no longer sets path until I did this. It looks like setting only on the login shell wasn't enough to hide the warning in other shells I opened. This fits with [how rbenv does the same thing](https://github.com/rbenv/rbenv/blob/master/libexec/rbenv-init#L74).

I'm way out of my depth here, so someone who knows about shell types should definitely review this.
sebhahn/pyenv,pyenv/pyenv,sebhahn/pyenv,sebhahn/pyenv,pyenv/pyenv,pyenv/pyenv